1. Technical Background
The present invention relates generally to medical devices, and more particularly to a self-expanding stent delivery catheter system having a rapid exchange configuration.
2. Discussion
Catheter systems are used in a variety of therapeutic applications, including many vascular treatments. Various types of catheters are available, such as balloon catheters for procedures such as angioplasty. Angioplasty can be used to treat vascular disease, in which blood vessels are partially or totally blocked or narrowed by a lesion or stenosis.
In many instances of vascular disease, a local area of a blood vessel may become narrowed. This narrowing is called a lesion or stenosis, and may take the form of hard plaque, cholesterol, fats, or viscous thrombus. Such a stenosis may cause heart attack or stroke, which are significant health problems affecting millions of people each year. Typical disease patterns involve stenosis development, causing a blockage or partial blockage at the site.
For example, various procedures are well known for addressing stenoses and opening body vessels that have a constriction due to plaque buildup or thrombus, etc. With such procedures, an expansive force may be applied to the lumen of the stenosis. This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to partially or completely re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. In the case of a blood vessel, this procedure is referred to as angioplasty. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel.
Often, it is deemed to be desirable to leave a device in place at the site of the expanded lumen of the stenosis, to provide support for the vessel wall at that location. Such a device may provide a scaffold type of structure about which, for example, endothelium development can occur to help repair the diseased, injured or damaged area. This scaffold device is referred to as a stent or endoprosthesis, and may have various designs, often having a resilient, flexible and cylindrical spring shape. In some cases, the stent which is a flexible cylinder or scaffold made of metal or polymers may be permanently implanted into the vessel. The stent tends to hold the lumen open longer, to reinforce the vessel wall and improve blood flow.
Stenting has come to be an accepted interventional medical procedure in many situations where vessels require support on a long-term basis. In operation, a catheter is used to transport the stent into and through a blood vessel, until the stent or the like is positioned at a desired location. Once at the desired location, the stent is deployed to provide internal support of the vessel or other treatment.
Some stents are deployed by an angioplasty balloon catheter, either during the angioplasty procedure or after a balloon has opened up the stenosis. These are called balloon-deployed or balloon-expandable stents. The balloon-expandable stents are forcibly expanded by a balloon or similar device through plastic deformation of the stent from a smaller to a larger diameter.
Another type of stent is of the self-expanding variety. Self-expanding stents tend to resiliently expand from an initial diameter, and must be held constantly in compression to remain at the initial diameter during delivery. Typically, a single cylindrical sheath or similar device over the stent is needed to hold the stent or other endoprosthesis at an initial diameter during passage through the body vessel. Once the treatment site is reached, the sheath or other device is withdrawn from around the stent, and the stent resiliently expands in place of its own accord.
This invention generally relates to stents which are of the self-expanding type. More particularly, the invention relates to self-expanding stents or other endoprostheses delivered in a compressed condition under radial compression, and which are deployed by removing a restraining member to permit the stent to resiliently expand and support a body vessel at that location. The stent may be made of a continuous strand shaped as a generally cylindrical member and having a plurality of coiling and/or undulating spring portions wound from the strand so as to impart the desired radial expansion force. The stent may also be formed of a metal or polymer tube, with cuts or slits removed to form a lattice.
As an example, the present invention will be described in relation to coronary, peripheral, and neurological vascular stenting treatments. The coronary procedure is often referred to as xe2x80x9ccoronary stenting.xe2x80x9d However, it should be understood that the present invention relates to any rapid exchange stent delivery system having the features of the present invention, and is not limited to a particular stent design or a particular deployment location.
Some catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and may deliver and deploy the stent near one end of the shaft. This end of the catheter where the stent is located is customarily referred to as the xe2x80x9cdistalxe2x80x9d end, while the other end is called the xe2x80x9cproximalxe2x80x9d end. The proximal end of the shaft may lead to a hub coupling for connecting the shaft and the lumens to various equipment. Examples of stents and catheters are shown in U.S. Pat. No. 5,843,176, entitled xe2x80x9cSelf-Expanding Endoprosthesis,xe2x80x9d issued to Weier on Dec. 1, 1998; and also U.S. Pat. No. 5,968,070, entitled xe2x80x9cCovered Expanding Mesh Stent,xe2x80x9d issued to Bley et al. on Oct. 19, 1999. In addition, U.S. Pat. No. 6,019,778 to Wilson et al., entitled xe2x80x9cDelivery Apparatus For A Self-Expanding Stentxe2x80x9d describes a self-expanding stent delivery system.
A common treatment method for using such a catheter is to advance the catheter into the body of a patient, by directing the catheter distal end percutaneously through an incision and along a body passage until the stent is located within the desired site. The term xe2x80x9cdesired sitexe2x80x9d refers to the location in the patient""s body currently selected for treatment by a health care professional. After the stent is deployed within the desired site, it will tend to resiliently expand to press outward on the body passage.
It is of course desirable to retain the stent securely in the proper position. The stent delivery system should also preferably protect the stent from damage or deformation during delivery. It is further desirable that the stent delivery system should be flexible and able to push through and traverse as many different anatomical arrangements and stenosis configurations as possible. Moreover, the stent delivery system should preferably have a positive mechanism for holding and then releasing and deploying the stent at the desired site. The stent delivery system also desirably includes a mechanism for securing the stent in the form of a sheath, capable of completely covering the compressed stent during insertion.
Stent delivery systems are often designed for the smallest possible outer diameter or profile at the distal end. This small profile may be preferred for access into small vessels following angioplasty, or during a procedure called xe2x80x9cdirect stentingxe2x80x9d where no angioplasty is performed.
In addition, the stent delivery system should provide for high visibility under fluoroscopy. Often the stent delivery system will be used in conjunction with an outer guiding catheter, which surrounds and guides the stent delivery system to the desired site. The visibility of the stent delivery system on a fluoroscope may be affected by the size of the lumen through which radiopaque contrast fluid is injected. This fluid is generally injected through the annular space between the guiding catheter and the stent delivery system. The visibility can therefore preferably be increased by further reducing the outer diameter of the stent delivery system.
Like many catheter systems, a stent delivery system is often used with a flexible guidewire. The guidewire is often metal, and is slidably inserted along the desired body passage. The catheter system is then advanced over the guidewire by xe2x80x9cback-loadingxe2x80x9d or inserting the proximal end of the guidewire into a distal guidewire port leading to a guidewire lumen defined by the catheter system.
Many catheter systems define guidewire lumens that extend along the entire length or almost all of the catheter. These catheter systems are described as xe2x80x9cover-the-wirexe2x80x9d catheters, in that the guidewires revisions inside a catheter lumen throughout the length of the catheter. Over-the-wire catheter systems provide several advantages, including improved trackability, preventing prolapse of the guidewire, the ability to flush the guidewire lumen while the catheter is in the patient, and the capability of easily removing and exchanging the guidewire while retaining the catheter in a desired position in the patient.
In some circumstances it may be desirable to provide a xe2x80x9crapid-exchangexe2x80x9d catheter system, which offers the ability to easily remove and exchange the catheter while retaining the guidewire in a desired position within the patient. In the balloon catheter arena, rapid exchange balloon catheters are disclosed in U.S. Pat. Nos. 5,380,283 and 5,334,147 to Johnson on Jan. 10, 1995 and Aug. 2, 1994, both entitled xe2x80x9cRapid Exchange Type Dilatation Catheter.xe2x80x9d Also, U.S. Pat. No. 5,531,690 to Solar on Jul. 2, 1996, entitled xe2x80x9cRapid Exchange Catheterxe2x80x9d describes a rapid exchange balloon catheter, as does U.S. Re. Pat. No. 36,104 to Solar entitled xe2x80x9cDilation Catheter With Eccentric Balloon.xe2x80x9d
In other words, rapid-exchange balloon dilatation catheters are capable of advancement into the vascular system of a patient along a pre-positioned guidewire, for balloon angioplasty or a similar procedure. The guidewire occupies a catheter lumen extending only through a distal portion of the catheter. With respect to the remaining proximal catheter portion, the guidewire exits the internal catheter lumen through a proximal guidewire port, and extends in parallel along the outside of the catheter proximal portion. Of course, the entire catheter and guidewire assembly is typically contained within the lumen of a guiding catheter, which retains a majority of the catheter and guidewire effective lengths together.
Because a majority of the guidewire is outside the catheter shaft, it may be manually held in place as the catheter is removed. Because the distal catheter guidewire lumen is shorter than the guidewire length that remains outside the patient, the catheter may be removed while also holding the guidewire, until the guidewire may be grasped at a point distal of the catheter. Completing a catheter exchange simply requires reversing the removal process. This rapid exchange technique enables a single physician to exchange balloon catheters, without requiring guidewire extension to temporarily double the guidewire length.
It may also be desirable to provide a self-expanding stent delivery system with a rapid exchange configuration. Prior self-expanding stent delivery systems are generally of the over-the-wire type. Such over-the-wire self-expanding stent delivery system includes an inner tubular body defining a guidewire lumen and providing a spine around which a compressed stent is mounted, as well as an outer sheath for containing the stent until it is pulled proximally to release the stent.
In contrast, most rapid exchange catheter systems incorporate a proximal guidewire port located at an intermediate point, between the catheter proximal and distal ends. However, the guidewire tube of a self-expanding stent delivery system is often surrounded by an outer sheath that must be capable of sliding motion to release the stent. Thus, a port or opening through both inner and outer tubes presents some alignment challenges, because the respective ports through the inner and outer tubes will tend to shift away from each other as the outer sheath is retracted.
One possible design is described in U.S. Pat. No. 5,690,644 to Yurek et al., entitled xe2x80x9cApparatus For Deploying Body Implantable Stent.xe2x80x9d Yurek et al. teaches a groove along an interior catheter that extends proximally to the proximal end of the catheter which cooperates with a long slot in the exterior catheter that likewise runs to the proximal end of the catheter. However, such a long groove and slot may tend to cause weakness in bending or pull strength. Unnecessary irritation of the vasculature may also be possible.
Accordingly, the present invention preferably provides a stent delivery system having a rapid exchange configuration for delivering and deploying a self-expanding stent. Among many kinds of modifications and features that may be provided with the stent delivery system of the present invention are a relatively small profile, several radiopaque marker bands indicating the positions of certain components, flexibility, minimization of any sharp edges when advancing or withdrawing the catheter system or when retracting the outer sheath, optimized longitudinal force transmission, materials selected for performance, affirmative release of the self-expanding stent when the sheath is retracted, as well as the safe and certain back-loading of a guidewire through the distal guidewire port and out the proximal guidewire port. Any shifting of the relative positions of the proximal ports in the inner and outer tubes should also be acceptably provided for. This stent delivery system preferably also provides stent position retention, as well as stent protection, during insertion of the catheter.
The stent delivery system also preferably has a high visibility arrangement for the injection of radiopaque contrast medium, facilitated by the relatively small reduced outer diameter of the stent delivery system including the sheath.